The use of radiation from lasers in medical and dental procedures has been known for some time, having been applied shortly after the invention of the laser in 1960. In 1961, medical researchers treated animal and human retinas and showed that a laser beam could induce a lesion on the retina for therapeutic purposes. Such laser eye surgery for detached retinas and other disorders is now routine in eye clinics throughout the world. In this application, and in others using laser beams, the laser beam is absorbed by the irradiated tissue causing heating, denaturing of protein, and tissue death. The results are therapeutic because of the formation of scar tissue, cauterization of the bleeding blood vessels, or the cutting away of diseased or damaged tissue.
Thus, in prior art applications of intense laser radiation, the laser was used to provide a directed source of the radiation whose thermal energy led to the pyrolysis of the organic matter. However, there are many situations where heating is not desired and is in fact harmful, and in those situations such lasers may not be used. As will be more apparent from the following, the present invention is directed to a technique for using radiation in a manner in which unnecessary heating and damage to surrounding organic tissue is avoided.
In the prior art, the intense laser radiation was generally in visible or infrared regions of the spectrum. For example, U.S. Pat. No. 3,769,963 describes an instrument for performing laser micro-surgery and describes the use of lasers for ophthalmology, dermatology, and experimental surgery. In this patent, a great deal of background information about laser treatments is provided, and the preferred wavelengths of light are stated to be 300-1000 nm although selective absorption of energy is noted in the range 200-3000 nm. In particular, selective absorption is noted in the visible range of 400-700 nm and in the infrared range at 1000 nm and 2000 nm.
Laser treatment of skin defects and lesions is described in U.S. Pat. No. 4,316,467 where a system is described for regulating the laser energy output in accordance with the absorption of the tissue being irradiated. Another reference describing lasers for medical and dental applications is U.S. Pat. No. 3,821,510. This patent describes a flexible laser beam transmitting device which can be held by hand and has certain adjustment features.
U.S. Pat. No. 4,273,535 describes a method for preventing tooth decay using giant pulses produced from a laser having an output wavelength of 1.06 micrometers (1060 nm). In particular, a flexible glass fiber is used as a laser beam guide for directing the laser energy from the laser source to the area to be irradiated.
In the prior art, the selectivity in absorption of different types of tissues has been noted, but the wavelengths used have been 200 nm and longer. Additionally, the only way to prevent irradiation (and its consequent damage) to nonselected areas surrounding the area selected for irradiation has been the use of a mask. Even with such a mask, heating of the target area is the primary mechanism for removal of organic matter. This means that surrounding areas will undergo some unavoidable heating and damage.
Accordingly, it is a primary object of this invention to provide an apparatus and method for efficient removal of organic biological material without heating or adverse effects to the areas of the material surrounding the area being irradiated.
It is another object of this invention to provide a technique and apparatus for removing organic biological material without using pyrolysis as the dominant mechanism for removal of the organic matter.
It is another object of the present invention to provide a technique and apparatus for decomposing an organic biological material by electronic excitation of the constituent bonds, followed by bond-breaking.
It is still another object of this invention to provide effective photoetching of the surface of biological material in a controlled manner.
It is a further object of this invention to provide a method and apparatus for photoetching the surface of organic materials in medical and dental applications.
It is another object of the present invention to provide focussed selective removal of organic matter, such as biological material, in a manner which does not require the use of heat, and without producing adverse thermal side effects.
It is another object of the present invention to provide a technique and apparatus for photoetching biological material which ablates the exposed surface of the material without significantly heating or otherwise damaging the remaining material, and without chemically altering the remaining material.